功率和谐波同步检测的马赫曾德调制器偏压控制技术

为了克服马赫曾德调制器工作点随温度、压力等外界因素的漂移，需要对它的直流偏压进行补偿。以往采用微扰信号谐波检测的方案偏置点定位精度高，但由于需要在回路中附加小幅抖动信号，会引入一定的噪声，影响信号的纯度；而功率检测的方案易受光源功率自身扰动的影响，稳定性不高，且偏置点定位性能差。提出了一种平均功率和谐波检测相结合的MZ调制器偏置点控制技术，通过谐波探测确定最佳工作点，并以电光调制器前后光功率比值作为基准值进行反馈控制，提高了偏压控制的定位精度和噪声性能，同时克服了激光功率自身扰动的影响。在此过程中还提出了一种通过操控误差信号实现偏置点任意调节的方案，实现了大范围灵活的偏置点控制。实验发现，所提出的方案具有定位精度高、稳定性好和偏置点调节范围广的优点，能够很好地满足马赫曾德调制器偏置点控制的要求。

Mach-Zehnder modulator bias controller based on power and harmonics synchronous detection

In order to overcome the drift of Mach-Zehnder(MZ) modulator operating point by the temperature, pressure and other factors, it is necessary to compensate the voltage shift of DC bias. The previous harmonic detection method based on small dither signal has the advantage of high bias point positioning accuracy. However, a certain noise will be introduced due to the additional small signal in the loop, which will affect the purity of the radio frequency signal. The power detection working point bias method is easily influenced by the power vibration of light source, which reduces the stability and positioning accuracy of the bias point. In this paper, a MZ modulator bias point control technique was proposed, combining the average power and the harmonic detection. The optimal operating point was determined by the harmonic detection, and the ratio of the optical power before and after the electro-optic modulator was used as the reference value in feedback control. It improves the positioning accuracy and the noise performance of the bias control. Meanwhile, it overcomes the influence of the disturbance of laser power. In this method, a scheme realizing the arbitrary adjustment of bias points by controlling the ratio of optical power was also proposed and large range flexible bias point control was realized. Experimental results show that the proposed scheme has the advantages of high positioning accuracy, good stability and wide bias point, which meets well with the requirements of the MZ modulator bias point control.